Inflammation is widely recognized to play a central role in the initiation and progression of tumor malignancy. Circulating macrophages are recruited by tumor cells through the secretion of soluble factors such as colony stimulating factor-1 (CSF-1) and C-C chemokine ligand 2 (CCL- 2). Through these mechanisms the macrophages are coerced to acquire a trophic phenotype accompanied by the release of soluble factors which promote angiogenesis, tumor cell invasion, and intravasation. Of particular interest is TAM-derived tumor necrosis factor-alpha (TNF-), which is believed to cause the downregulation of cell adhesion molecules (e.g. E-cadherin) in tumor cells, increasing cell motility and entry into the circulation. Understanding of such relationship is key for the design of anti-metastatic therapeutics. However, much of the data reported in this field has been performed in xenograft models and/or 2D cultures; which are limited by the number of controllable variables, extrapolation to human tumor physiology, and not amenable for a high-throughput design. In this proposed research training fellowship, the goal is to create an optimal in vitro model to study the tumor microenvironment. The first aim seeks to gain a better understanding of the behavior of tumor cells, endothelial cells, and TAMs in a 2D environment through an array of classical co-culture experiments. Results of this aim will generate relevant design parameters which will be implemented in the second aim of this project, which combines principles of microfluidics with tissue engineering to create a 3D tissue model of the tumor microenvironment with perfused human capillaries. This model will be able to replicate the physiology of the in vivo tumor microenvironment; thus providing relevant physiological results. Most importantly, the impact of creating an in vitro 3D metastasis model with perfused human capillary bed could significantly enhance high-throughput anti-metastatic drug screening.